The objective of this contract is the evaluation of a high-frequency audiometer and transducer assembly to determine its validity and reliability for measuring hearing thresholds in humans at frequencies beyond the limits of conventional audiometry. This will be accomplished by testing for reliability and procedural considerations with normal-hearing patients and by testing drug- and noise-exposed patients to evaluate the utility of high-frequency audiometry. Additional research will be performed to define the limits of using the calibration procedure with respect to ear canal size, to assess the feasibility of measuring auditory brainstem responses to high-frequency stimuli, and to determine threshold adaptation and temporal integration by employing high-frequency sounds.